Abstract

A large solid-angle array of low pressure multiwire proportional counters has been constructed as part of the Atlas Positron EXperiment (APEX). Eight three-element trapezoidal counters provide 360-degrees coverage in phi and 20-degrees-68-degrees coverage in theta. Angle sensitivity in theta is provided by a transmission-line delay cathode, while the segmentation provides angle sensitivity in phi. Sample data are presented from the 1450 MeV U-238 + Ta-181 reaction.